When trying to start the recovery process in a Standby Database, the following error message appears:

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT
*
ERROR at line 1:
ORA-01153: an incompatible media recovery is active


The cause of the ORA-01153 can translate into a RMAN recovery or backup session.
If we see that although a recovery session already exists but the Standby Base is not synchronizing, then we can stop the current session with the following command:

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

Database altered.


Then we can run the recovery start command again and we can see that now no error message is shown:

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;

Database altered.


Now the synchronization process must continue without problems.